Controlled and fixing liquid developer for electro-photography and electroradiography



United States Patent 3,193,649 CGNTRGLLED AND FEXLN'G LlQUlD DEVELGPERFUR ELEEITRU-FHQBTUGRAPHY AND ELECTRQ- RADIOGRAPHY Kenneth ArchibaldMetcalfe, Graymore, South Australia, and Robert John Wright,Plectorville, South Australia, Australia, assignors to The Commonwealthof Australia, care of the Secretary, Department oi Supply, Melhonrne,Victoria, Australia No Drawing. Filed May 12, 1969, Ser. No. 28,524Claims priority, application Australia, May 13, 1959, 48,757/59 13(Ilaims. (Cl. il737) This invention relates to the development orelectrostatic images produced by electrostatic, electro-photographic orelectro-radiographic means.

According to United States Letters Patent No. 2,907,674 liquiddevelopers are described which utilize control and fixing agents tocontrol the charge on pigment particles and to fix the particles to thearea where they are de posited.

The present invention is directed to the use of particular groups ofsubstances which are capable of acting both as control and fixing agentsin liquid development processes, the object of the invention being toprovide a group or" substances which will give a selection ofcharacteristics to meet different developing conditions.

in electro-photography it is customary to use a plate or paper having onit a layer of photoconductive material, such as amorphous selenium whichin the dark will accept and hold an electrostatic charge, this platebeing then exposed in any manner to vary the charge thereon according tothe pattern of exposure to light or other influence and the plate issubsequently developed by applying thereto a powder having a charge, sothat when the powder is applied to the plate it will be accepted by theplate in conformity with the charge on the various sections of theplate, this then producing an image in the powder.

One of the diliiculties with this .type of development has been to beable to distribute the powder finely and in uniform consistency becauseobviously if the powder is unevenly applied, the image will similarly beunevenly built up and will not be a time picture of the originalexposure. Another difiiculty is to fix the powder on the plate in apermanent manner because obviously in the industrial application ofelectro-photography it is essential that a permanent image will result,this permanence being at the present time usually obtained by includinga resin which, after the dust has been deposited on the plate, can befixed by subjecting the resin to heat. Another diiiiculty is to ensurethat the powder has the correct polarity in relation to the charge onthe plate and where the powder comprises more than one material which itis desired to co-deposit for example so as to form a mixed colour, toensure that the plurality of materials all have the same polarity inrelation to the charge on the plate.

The objects of the present invention are to improve the image and toproduce it in a better manner this being achieved by wet development or"the image, the invention being directed to the productionot anelectrostatic image on a suitable surface which is then developed onthatsurface or transferred to another surface, and developed by wettingthe surface with a carrier liquid having an electrical resistivitysufficiently high to prevent destruction of the electrostatic image.This liquid carries dispersed in it a pigment which has a charge of thecorrect polarity or has added to it a control agent to modify thecharge, to act in conjunction with the electrostatic image on thesurface to develop the image, and a fixing agent to render ?alented Aug;3, 1965 "ice the pigment fast when the carrier liquid is evaporated orremoved.

A most important aspect will at once be apparent that where the pigmentcomprises a plurality of materials, the control agent will act to confera similar polarity'and magnitude of charge on each of the said materialswhich makes possible the mixing of materials with different bull;chemical properties and different bulk physical properties for examplethe co-depositionof two or more colours to produce a mixed colour ofdesired tone shade or tint.

Where the pigment material is carried in a neutral high resistanceliquid which will not destroy the charge on the plate, at least duringthe development period, the whole of the image will be uniformlysubjected to the liquid in which lie colour material is evenly andgenerally thinly dispersed and this will result in rapid depos tion ofthe colour material in a density varying in proportion to the chargeheld by the various parts of the image, and as the suspending liquid ispreferably a highly volatile one, evaporation of this liquid fromthedeveloped image will rapidly leave the image in a dry condition so thatif a fixing agent has been added to the carrier liquid or if thedeveioper has that characteristic, the pigment is left adher ing rigidlyto the surface which has been developed. The high resistivity insulatingliquid also allows the particles carried by it to have and retain thenecessary electrical characteristic, which characteristic can be variedby charging the liquid or by adding a control agent operative either onthe liquid or the suspended matter. I

When liquid development was first envisaged, it was suggested that thepigment particles should be suspended in a carrier liquid having anelectrical resistivity sufficiently high to prevent destruction of theelectrostatic image being developed such as the image on aphotoconductor surface.

This was the state of the art at the time of filing the aforesaid UnitedStates Patent application. That specification however takes theliquiddevelopment process to a greatly improved form in that it teaches theart of controlling the charge on the pigment particles duringdevelopment and also the art of simultaneously automatically arrangingthe conditions whereby the pigment particles are fixed to the surfacebeing developed.

The advantages of using a control substance is that the particles of thepigment material, as well as the impurities present, are given aspecific charge value and can thus be closely controlled by theirmovements. 7

The advantages of the automatic fixing of the particles are obvious,doing away with subsequent treatment and similar problems.

The present invention extends further the range of substances which canbe used for specific types of development and relates to thosesubstances which act as both control and fixing agents. In general theinvention comrises mixtures of colourin material with combined con- B ithas been shown that the density of the image deposit may be varied byvarying the ratio of the pigment material to the carrier liquid mixtureswhere the ratio of pigment material to the carrier liquid mixtures wasequal to or greater than '1 to parts by weight. Micronized powders haveproved to be highly satisfactory, the particles having a mean diameterbetween 1 tenth micron and 10 microns. Larger particles can be usedwhere the resolution desired in the image is not critical.

An essential feature of the pigment-resin-carrier combination is thatthe combination should be a good insulator. Combinations of lesserinsulation tend to discharge the electro-photograph without properlydeveloping it. The pigment itself however need not be an insu'lator aslong as the remaining components are; for example, use of metallicparticles is permissible.

The invention is considered to function in the following manner: eachsmall volume of carrier liquid has dispersed in it a number of thecontrolled particles which automatically have a charge of magnitude andpolarity governed by the control agent. As the liquid contacts the platethe particles are given up to the charged areas on the plate, theattraction between the particles and the charged areas being strongerthan that between the carrier liquid and the particles. The liquid picksup and carries away any particles which may tend to settle on unchargedareas, or if the plate is developed face down these particles gravitateaway. If the liquid is selected to have a high specific gravity thepigment material may be more readily dispersed and utilised fordevelopment because of greater buoyancy.

It is necessary for the fixed image to be permanent and stable under theconditions normally encountered by printed materials, that it should notdecompose or bleach by light or be readily attacked by micro-organisms.The completed image should also be relatively hard but sufficientlytough to be resistant to chipping under conditions of handling and use.The pigment material and fixing agent must be free of any reactivematerial such as acids which deleteriously react with the paper or otherbases to'cause' deterioration in storage (unles there is an end userequiring reactivity to acid).

It is of course necessary that the toner have a prescribed colour eitherby virtue of the pigment or the bonding material. For general use incopying and printing a dense black is required but sometimes coloured,images are Wanted. The pigment material must be capable of dispersion tofine particle size such as 0.1 to 10 microns. In lithographicapplications the pigment material must be transferable to or developableon a paper or metal master and when in position be ink accepting.

The compositions of the present invention meet the varied and exactingrequirements mentioned above and comprise developers capable ofproducing permanent images on cloth, paper, plastic and metal surfacesand are also capable of forming printing images which are wettable bylithographic inks and are capable of bonding to both metal and paper'oflset plates to form durable printing plates for printing thousands ofcopies.

The characteristics of the substances forming the basis of thisinvention are as follows:

The substance must be capable of being softened or dissolved so that itcan be applied as the outer phase to pigment particles (i.e., it coatssaid particles).

The substance must be such that it can remain as the outer phasethroughout the development time to ensure that the substance is theelectrically dominating factor but at the same time the substance mustbe capable of being held in a softened or partly dissolved tate so thatthere is the required tackiness to allow the substance to be attached tothe surface being developed and which on evaporation of the carrierliquid will then harden or otherwise change to fix the image.

Amongst the control agents, which also act as fixing agents, fallingwithin the above category we have the rubber solutions which are a blendof natural and synthetic rubber uch as the Dunlop Rubber solution, thesafllower oil modified alkyds, the linseed oil modified penta-erythritolalkyds, and polystyrene.

The following examples are given to show how these various substancescan be used as combined control and fixing agents.

l EXAMPLE 1 Rubber Synthetic and natural rubbers have been found to beuseful in the compounding of liquid developer bases. These materialshave been tested in conjunction in the form of a proprietary adhesive ofthe following composition:

Grms. Natural rubber 1O Hycar l Benzene 90 This material containssufiicient solvent to wet the pigment and form a developer paste ofsuitable consistency for hand grinding.

The mixed synthetic and natural rubbers would be expected to be usableas combined control and fixing agents due to the different solubilitiesof the two components. Thus it could be expected that Hycar would undercertain conditions be usable as a control agent While the natural rubbercould be expected to have fixing properties.

As it is desired to use the mixed rubbers as combined control and fixingagents, solvent or carrier choice becomes somewhat critical. It wasfound for instance that while satisfactory dispersions of rubber baseddevelopers could be made in Shellite, the control properties of suchdevelopers were somewhat erratic due to the degree of solution of Hycarin Shellite. This resulted in a developer which deposited on both imageand non-image areas, with a consequent serious loss of definition. Thedesired solvent selectivity was found to be available intrichlorotrifiuoroethane (Freon 113) which was consequently used as thebase liquid for subsequent tests.

Varying quantities of the rubber mixture described were blended withcarbon black using hand grinding techniques. These results are tabulatedbelow.

Development Rubber Carbon Freon results on zinc 501., Black, 113, ml.oxide paper grrns. grins. (neg. charge) 2 100 Positive unfixed image. 2100 Do. 2 100 Positive partially fixed image. 20 1 100 Positive fixedimage.

EXAMPLE 2 Safilower modified alkyd resins The safflower oil modifiedalkyd resins are suitable for use in developer and coating formulations.

One resin of this group which is particularly eifective is Rhodene L/60by the Polymer Corporation This is safflower oil modified alkyd resin ofoil length acid value 6-10 and specific gravity 0940-0950.

Although the resin contains only solids it was found to be necessary toadd extra solvent in order to hand grind the desired resin/ pigmentratio.

The formulations used was as follows:

Grins.

Rhodene L45/60 l0 Mineral turpentine Carbon black The pentaerythritolresins have been found useful as fixing agents due to their relativesolvency in the various carrier liquids. Pentaerythritol alkyd resinsact as control agents with enough solubility to act also as fixingagents.

A suitable resin is that sold by the Polymer Corporation under the tradename Rhodene PC2/70.

This is a linseed oil modified pentaerythritol alkyd resin, of oillength 70%, acid value 6-10 and specific gravity 20 C. 0955-0965.

This resin, supplied as a 70% solution in mineral turpentine, is of varylong oil length, and provides a suitable combination of hardness andflexibility.

In compounding the base, Rhodene PC2/70 was used in two different forms.The first was the as-received material containing mineral turps, whichwas hand ground with pigment to form a developer base. Proportions usedwere as follows:

Grms.

Rhodene PC2/70 (as received) 10 Carbon black a- 14 The second form wasthe base resin which had dried on standing to be virtually pure resin atleast partly polymerised. This material was heat-blended in mineralturps to form a solution before hand-grinding with pigment. Proportionsused were as follows:

Rhodene PC2/70 (dried) 10 grms. Mineral turpentine 10 grms. Heat blendedCarbon black 20 grms.

Materials from each of the preceding formulations were used separatelyas liquid developer bases. These were dispersed in various carrierliquids and used as liquid developers. They were found to dispersereadily in Shellite, so this was the preferred carrier liquid.Dispersions of various concentrations were tested, generally 0.5 to 5.0grms. developer base/IOO/ml. Shellite was found to be the mostsatisfactory range of concentration suitable for development of imageson zinc oxide paper.

Rhodene PC2/7O base developers were found to be satisfactory fordevelopment of zinc oxide image surface, that is the resin acts as apositive control agent. it also exhibited strong fixing properties. ThusRhodene PC2/70 can be classed as a resin useful as a combined controland fixing agent when used in conjunction with the carrier liquidShellite.

EXAMPLE 4 Polystyrene solutions The standard technique of grinding thedissolved resin or the like with the pigment was used and therefore thefirst requirement was the solution of the polystyrene in a suitableliquid. The most promising liquids were the aromatic andaromatic-containing hydrocarbons and hy- I drocarbon mixtures toluene,benzene and mineral turpentine. Solutions of the polystyrene in each ofthese liquids were therefore prepared and each was then separatelyground with carbon black to form a developer base.

A polystyrene/mineral turpentine/pigment developer base was formed asfollows:

The polystyrene was dispersed in mineral turpentine and also in benzene,and used as a developer. A positive fixed image was obtained.

When polystyrene is dissolved in toluene as the control agent (thepigment being hand ground with the polystyrene sol to form a developerbase, and then dispersed separately into the carrier liquids) it wasfound that dispersed in mineral turpentine it formed a stable suspensionwhich gave a positive partially fixed image, but when dispersed in asmall quantity of mineral turps, and benzene was then added, a developergiving a high quality fixed image results.

if Shellite is added, the developer is also satisfactory but must beused immediately. A further series of tests was carried out usingbenzene as the solvent.

Polystyrene in benzene was tested in various carrier liquids and it wasfound that in mineral turpentine it dispersed to give a stablesuspension which gives a high density positive permanent fixed image,and in perchloroethylene it gives a stable dispersion which gives apositive partially fixed image.

A method of preparing the developer base is as follows:

Polystyrene is first dissolved in benzene. l0 grms. polystyrene weredigested in 70 grms. benzene and concentrated to a solution of totalweight 47 grms., that is the final solution contains 10 grms.polystyrene and 37 grms. benzene or 21.3% polystyrene. Various weightsof carbon black were ground with fixed portions of the solution to formdeveloper bases of various pigment concentrations. The optimum was foundto be a blend of polystyrene and benzene, and carbon black in a ratio ofabout 7:5 grams as follows:

Grms. 21% polystyrene in benzol sol 7 Carbon black 5 Dispersed l grm.paste/ grms. mineral turpentine.

Polystyrene base developer prepared as above gave a positive controlwith a heavy well fixed image deposit.

What is claimed is:

1. A controlled and fixing liquid developer for electric-photography andelectro-radiography comprising a particulate pigment substance, acontrol agent coating the said particulate substance and constituting acontrol coating thereon, said control agent influencing theelectrostatic behavior of said substance said control agent including incombination natural and synthetic rubbers, said agent forming a basewith the pigment substance, and an electrically insulating carrierliquid for the coated pigment substance, said control agent beingsufficiently soluble in said liquid to maintain the outer surface of thecontrol coating in a partly dissolved state to constitute a fixingagent, said agent being sufiiciently insoluble in said liquid to insureretention of at least part of the control coating on said substancethroughout a developing operation, said coated pigment substance beingsuspended in the carrier liquid.

2. A developer as claimed in claim 1 wherein said liquid istrichlorotrifluoroethane.

3. A developer as clain ed in claim 1 wherein said control agent is ablend including said rubbers and carbon black in a proportion of 20grams of rubber to 2 grams of carbon black to millilitres of saidliquid, said liquid being trichlorotrifiuoroethane.

i. A controlled and fixing liquid developer for elec trio-photographyand electro-radiography comprising a particulate pigment substance, asafilower oil modified alkyd resin constituting a control agent coatingthe said particulate substance and further constituting a controlcoating thereon, said control agent influencing the electrostaticbehavior of said substance, said agent forming a base with the pigmentsubstance, and a carrier liquid for the coated pigment substance, saidcoated pigment substance being suspended in the carrier liquid, saidcontrol 7 agent being sufficiently soluble in said liquid to maintainthe outer surface of the control coating in a partly dissolved state toconstitute a fixing agent, said agent being sufiiciently insoluble insaid liquid to insure retention of at least part of the control coatingon said substance throughout a developing operation.

5. A controlled and fixing liquid developer for electrio-photography andelectro-radiography comprising a particulate pigment substance, acontrol agent coating the said particulate substance and constituting acontrol coating thereon, said control agent influencing theelectrostatic behavior of said substance, said agent forming a base withthe pigment substance, and a carrier liquid for the coated pigmentsubstance, said control agent being suffic'ently soluble in said liquidto maintain the outer surface of the control coating in a partlydissolved state to constitute a fixing agent, said agent beingsufiiciently insoluble in said liquid to insure retention of at leastpart of the control coating on said substance throughout a developingoperation, said coated pigment substance being suspended in the carrierliquid; said control agent being a blend including a safilower oilmodified alkyd resin and mineral turpentine, said liquid being analiphatic hydrocarbon solvent.

6. A controlled and fixing liquid developer for electric-photography andelectro-radiography comprising a particulate pigment substance, acontrol agent coating the said particulate substance and constituting acontrol coating thereon, said control agent influencing theelectrostatic behavior of said substance, said agent forming a base withthe pigment substance, and a carrier liquid for the coated pigmentsubstance, said control agent being sufiiciently soluble in said liquidto maintain the outer surface of the control in a partly dissolvedstate, said agent being sufiiciently insoluble in said liquid to insureretention of at least part of the control coating on said substancethroughout a developing operation, said coated pigment substance beingsuspended in the carrier liquid, said control agent being a blendincluding a safilower oil modified resin, carbon black and mineralturpentine in a ratio of 10:20:10 grams, said liquid being an aliphatichydrocarbon solvent in an amount of 100 millilitres for about 40 gramsof said blend.

7. A controlled and fixing liquid developer for electric-photography andelectro-radiography comprising a particulate pigment substance, acontrol agent coating the said particulate subtance and constituting acontrol coating thereon, said control agent influencing theelectrostatic behavior of said substance, said agent forming a base withthe pigment substance, and a carrier liquid for the coated pigmentsubstance, said control agent being suificiently soluble in said liquidto maintain the outer surface of the control coating in a partlydissolved state, said agent being sufiiciently insoluble in said liquidto insure retention of at least part of the control coating on saidsubstance throughout a developing operation, said coated pigmentsubstance being suspended in the carrier liquid, said control agentincluding a pentaerythritol alkyd resin.

S. A developer-as claimed in claim 7 wherein said resin is a linseed oilmodified pentaerythritol alkyd resin, said liquid being an aliphatichydrocarbon solvent.

9. A developer as claimed in claim '7 wherein said control agent is ablend including a linseed oil modified pentaerythritol alkyd resin,mineral turpentine and carbon black in a ratio of about 10:10:20 grams,said liquid being an aliphatic hydrocarbon solvent.

13. A controlled and fixing liquid developer for electric-photographyand electro-radiography comprising a particulate pigment substance, apolystyrene agent coating the said particulate substance andconstituting a control coating thereon, said control agent influencingthe electrostatic behavior of said substance, said agent forming a basewith the pigment substance, and a carrier liquid for the coated pigmentsubstance, said control agent being suiiiciently soluble in said liquidto maintain the outer surface of the control coating in a partlydissolved state, said agent being sufiiciently insoluble in said liquidto insure retention of at least part of the control coating on saidsubstance throughout a developing operation, said coated pigmentsubstance being suspended in the carrier liquid.

1 A developer as claimed in claim 19 wherein said control agent is ablend including polystyrene and hydrocarbon solvent.

12. A developer as claimed in claim 10 wherein said control agent is ablend including polystyrene and benzene, and carbon black in a ratio ofabout 7:5 grams, said liquid being mineral turpentine.

13. A method of fixing a developer substance, which is suspended in anelectrically insulating liquid carrier, on a surface having anelectrostatic image; said method comprising coating said substance witha material influencing the electrostatic behavior thereof and whichsubstance is partly soluble in said carrier dispersing the thusly coatedsubstance in said carrier whereby said material is rendered tacky,applying said carrier with the coated developer substance to saidsurface to deposit said coated developer substance on said image, andphysically bonding said developer substance to said surface by means ofsaid material.

References Cited by the Examiner UNITED STATES PATENTS 2,286,762 6/42Risher 117162 X 2,381,753 8/45 lrion 26033.8 X 2,891,911 6/59 Mayer etal 11717.5 X 2,899,335 8/59 Straughan 11737 2,907,674 10/59 Metcalfe etal 117--34 2,940,934 6/60 Carlson 117l7.5 X 3,010,842 11/61 Ricker117-37 3,080,250 3/63 Claus 11717.5

WILLlAM D. MARTIN, Primary Examiner.

RICHARD D. NEVIUS, Exaliziner.

1. A CONTROLLED AND FIXING LIQUID DEVELOPER FOR ELECTRIC-PHOTOGRAPHY ANDELECTRO-RADIOGRAPHY COMPRISING A PARTICULATE PIGMENT SUBSTANCE, ACONTROL AGENT COATING THE SAID PARTICULATE SUBSTANCE AND CONSTITUTING ACONTROL COATING THEREON, SAID CONTROL AGENT INFLUENCING THEELECTROSTATIC BEHAVIOR OF SAID SUBSTANCE SAID CONTROL AGENT INCLUDING INCOMBINATION NATURAL AND SYNTHETIC RUBBERS, SAID AGENT FORMING A BASEWITH THE PIGMENT SUBSTANCE, AND AN ELECTRICALLY INSULATING CARRIERLIQUID FOR THE COATED PIGMENT SUBSTANCE, SAID CONTROL AGENT BEINGSUFFICIENTLY SOLUBLE IN SAID LIQUID TO MAINTAIN THE OUTER SURFACE OF THECONTROL COATING IN A PARTLY DISSOLVED STATE TO CONSTITUTE A FIXINGAGENT, SAID AGENT BEING SUFFICIENTLY INSOLUBLE IN SAID LIQUID TO INSURERETENTION OF AT LEAST PART OF THE CONTROL COATING ON SAID SUBSTANCETHROUGHOUT A DEVELOPING OPERATION, SAID COATED PIGMENT SUBSTANCE BEINGSUSPENDED IN THE CARRIER LIQUID.
 13. A METHOD OF FIXING A DEVELOPERSUBSTANCE, WHICH IS SUSPENDED IN AN ELECTRICALLY INSULATING LIQUIDCARRIER, ON A SURFACE HAVING AN ELECTROSTATIC IMAGE; SAID METHODCOMPRISING COATING SAID SUBSTANCE WITH A MATERIAL INFLUENCING THEELECTROSTATIC BEHAVIOR THEREOF AND WHICH SUBSTANCE IS PARTLY SOLUBLE INSAID CARRIER DISPERSING THE THUSLY COATED SUBSTANCE IN SAID CARRIERWHEREBY SAID MATERIAL IS RENDERED TACKY APPLYING SAID CARRIER WITH THECOATED DEVELOPER SUBSTANCE TO SAID SURFACE TO DEPOSIT SAID COATEDDEVELOPER SUBSTANCE ON SAID IMAGE, AND PHYSICALLY BONDING SAID DEVELOPERSUBSTANCE TO SAID SURFACE BY MEANS OF SAID MATERIAL.